Microshocks

In certain circumstances, a person exposed to a high electric field could experience small spark discharges on touching other objects. 

This can happen two different ways.  In both cases the common feature is the person touching an object, where one is at earth potential and the other, which is not earthed, has been raised to a higher potential by the electric field.  When the person touches the object, charge flows so as to equalise the potentials, and this charge, concentrated on the small area of skin where contact is first made, creates the microshock. 

In the diagram below, on the left is the situation where the person is grounded through their feet and then touches an ungrounded object.  On the right is the other situation where the person is isolated from ground (because they are wearing insulating footwear or are standing on an insulating surface) then touches a grounded conducting object. (more detail on how the charge actually flows when this happens)

diagram showing how microshocks arise

The sensation of a microshock is similar to that caused by the static discharges commonly experienced in dry atmospheric conditions after frictional contact with a nylon carpet or car seat. Normally, any sensation is confined to the momentary spark discharge as contact is made or broken.

The size of microshocks

The size of a microshock depends on the size of the objects concerned and how well grounded or insulated they are, as well as the field, so it is not possible to set a simple field limit to prevent them.  Generally speaking, below 5 kV/m they are not a problem. Above 5 kV/m they may start being painful, depending on the individual situation.  See:

How sensitive people are to microshocks

There are data from America showing that in a field of 5 kV/m, for example, around 80% of people will perceive a microshock when touching a grounded object, but only about a quarter will describe it as annoying.  see these measurements in more detail

Microshocks and bicycles

One particular way a microshock can be experienced is by riding a bicycle under a high-voltage power line.